1. Field of the Disclosure
The present disclosure relates to a gap adjusting method in a trip mechanism of a molded case circuit breaker, and particularly, to a gap adjusting method which easily adjusts a gap between a bimetal and a crossbar by using a gap adjusting block and an adjusting screw in a trip mechanism of a molded case circuit breaker without a separate additional device, thereby enhancing a consistency of quality and assembly.
2. Background of the Disclosure
Generally, a molded case circuit breaker is mainly provided in a switchboard in power distribution equipment of a factory, a building, etc. In an unloaded state, the molded case circuit breaker acts as a switchgear that supplies or cuts off power to a load. In use of a load, when a high current exceeding a load current flows because an error occurs in a load electric circuit, the molded case circuit breaker acts as a circuit breaker that cuts off power supplied from a power source to the load so as to protect a power line of an electric circuit and elements of the load.
The molded case circuit breaker is formed in a structure where a switching mechanism, a trip mechanism, and an extinguishing device are coupled to each other in an external box formed of an insulating material. FIG. 1 illustrates a cross-sectional view of a related art molded case circuit breaker. The switching mechanism includes a power terminal 1 that is supplied with power, a fixed contactor 2 and a movable contactor 3 that transfer the power to a load, and a lever 4 that connects or disconnects the movable contactor 3 to or from the fixed contactor 2 to operate a circuit in a closed state or an open state. Also, the trip mechanism includes a heater 5 that detects an overcurrent, a bimetal 6 that is connected to the heater 5 and is bent by heat of the heater 5, and a crossbar 7 that binds the switching mechanism so as to maintain the closed state or the open state.
FIG. 2A is a front view of a related art trip mechanism, and FIG. 2B is a side view of the related art trip mechanism. Under an overload condition, the trip mechanism of the molded case circuit breaker detects an overload by using the bimetal 6 in which two members having different heat conductivities are bonded to each other, and breaks an electric circuit. When a high current flows like short circuit or ground, the trip mechanism breaks the electric circuit in a method using the principle of a magnet which instantaneously absorbs the high current to generate a magnetic field. Here, it is necessarily required to appropriately adjust a gap between the crossbar 7 and the bimetal 6, and in detail, a gap between the crossbar 7 and a rivet 8 coupled to the bimetal 6, so as to detect an overcurrent and appropriately break a power line.
FIG. 3 is a flowchart of a related art gap adjusting method, and FIG. 4 illustrates a gap adjusting operation.
The related art gap adjusting method will now be described. In a state where a circuit breaker is switched on, the rivet 8 assembled with the bimetal 6 is closely adhered to the crossbar 7 (FIG. 4A). The heater 5 generates heat when a predetermined overcurrent (a setting current) is applied to the circuit breaker, and the heat is conducted to the bimetal 6, whereby the bimetal 6 is bent. At this time, since the rivet 8 may freely move in a state of being assembled with the bimetal 6, the rivet 8 slides in a direction opposite to a bending direction of the bimetal 6, and maintains a state of being closely adhered to the crossbar 7 (FIG. 4B). After an overcurrent is applied and then a predetermined time (a setting time) elapses, the application of the overcurrent stops, and the rivet 8 is welded to the bimetal 6 by using a laser. Subsequently, the bimetal 6 is cooled to return to a normal state, and thus, a gap is formed between the crossbar 7 and the rivet 8 (FIG. 4C).
Here, a bending amount of the bimetal 6 is changed according to a current which is applied for gap adjustment. That is, as an applied current increases, a gap increases, and as the applied current decreases, the gap decreases. A setting of a setting current (i.e., an applied current) is determined by a trip stroke and trip load including an amount of invalid displacement in the switching mechanism of each product. Here, the trip stroke denotes a rotation distance from a position of the crossbar 7 in a normal state to a position in which the crossbar 7 rotates and thus the switching mechanism is released. Also, the trip load denotes a load which is applied to the crossbar 7 when the switching mechanism is tripped. The setting current is determined by measuring the trip stroke and trip load of the switching mechanism, and a gap suitable for the circuit breaker can be optimized by applying the setting current to the circuit breaker for a setting time.
In the related art, the heater 5 generates heat by applying a current, and the bimetal 6 is bent by the heat. A gap adjusting operation is performed in a state where the bimetal 6 is bent. A current several hundred times higher than a rated current of a product is applied within several seconds for performing the gap adjusting operation according to the standard, and for this reason, quality problems such as a color change of an element and an expansion of a load terminal caused by heat transfer occur.
Moreover, much cost for constant current test equipment for applying a current, laser welding equipment and a cooling device for fixing a rivet after a gap is adjusted, and facilities of the cooling device for restoring a bent bimetal after the gap is adjusted is expended, and maintenance cost is also expended.
When a change of a gap is needed due to a 4M change, it is difficult for a worker to easily change an amount of applied current or a time.